The present invention relates to a multi-stage wire drawing machine and, in particular, to a drum therefor having a plurality of sheaves over which the wire is pulled.
Multi-stage wire drawing machines, in general, comprise at least one pair of wire pulling drums over which the wire is pulled in alternate directions. Each of the drums is formed either as a continuous conical pulley or as a plurality of individual sheaves and is each preceded and followed by a wire extending die, over which the wire is sequentially attenuated and extended. In German Patent No. 940,974, an earlier machine having a drum is shown in which the wire first runs on the small diameter of a conical drawing die. Such apparatus have the advantage of requiring only a very small space. On the other hand, they possess a considerable drawback in that particularly thick wires are not uniformly stretched throughout their cross-section. In such machines the thick wire is inordinately attentuated in its peripheral or outer fibres and thus is drawn with inherent stressed conditions. In order to avoid this defect, apparatus has been designed having a drum provided with multiple-stage draw die over which the wire is sequentially passed. Such a device shown in U.S. Pat. No. 1,973,596. In this patent, the drum is formed with a plurality of sheaves, each preceded by an individual wire extending die, which sheaves have the same uniform outer diameter. In this construction, the first and the last of the sheaves, in the direction of wire passage, are driven and the intermediate sheaves are coupled by a planetary gear transmission which includes a gear rim formed on each of the sheaves and a bevel pinion mounted rotatably therein. The sheaves thereby, have a complicated structure and their drive is most difficult. As a consequence the apparatus of the type shown in the aforementioned U.S. Patent has not found their way into practical use for this reason, as well as for other economical reasons related to their complex operation and maintenance.
Another multi-stage wire drawing machine has become known through the German Patent No. 1,144,673 in which all of the individual draw die plates are provided with the same, but relatively large diameter. Because of the extremely large diameter of the draw die plates used in this Patent, the advantage of a minimum space requirement is destroyed. Further, each of the draw die plates are provided with only two bearing points, and additional shafts must be mounted within the draw plates by the use of two additional friction bearings located within bores inside the draw die plates. These shafts are required to carry at each of their ends a spur gear having different numbers of teeth. The design of this latter German Patent is highly complicated and results in the formation of a number of wear points causing early breakdown of important parts. This greatly adds to the cost of the machine and its continued operation by the need of maintaining large stock of parts so that the machine may be easily and quickly repaired without extensive downtime.
In summary, it is observed that all of the known apparatus have numerous disadvantages, either draw die plates of too small diameter, or when the diameter is dimensioned adequately, the cost of construction, the complexity of the machine and the space requirements are no longer within reasonable limits. Furthermore, due to the wear on the die surfaces of the draw plates, in the machines heretofore know, their graduation has to be designed with a ratio or difference relative to the rated wire extension which disadvantageously results in the accumulation of a large slip factor. In particular the slip factor is most undesirable in those cases wherein the machines are provided with a rather large number of pulls on the wire. Consequently, a considerable loss of power results in the operation of the machine, coupled with considerable wear on the surfaces of the draw die plates and actual damage to the surface of the wire. An attempt has been made to reduce the degree of slippage and therefore the loss of power. Reference is made to the Journal "Draht" Vol. 5, 1954, No. 8, Article on: "New Multiple Wire Drawing Machines With Reduced And Controlled Slip Of The Wire On The Draw Plates" by Walther Nacken in which is disclosed the fact that before and after each sheave a die or a "cone" is located and that each plate or sheave pulls the wire from the die or cone preceding it and supplies the wire to the next following die or cone. Each of the dies or cones has a tapered bore in which the wire is compressed and reduced in diameter and thus extended by a predetermined percentage. Attention should be particularly made of FIG. 1 of said Nacken's article wherein a reduction of slip is illustrated as being attained only in coarse and rough stages and only between two neighboring pairs of said cones. Within each pair of said cones, however, undesirable slip is encountered which has a greater degree than heretofore.
It is the object of the present invention to provide a wire drawing device overcoming the disadvantages and defects of the prior art.
It is another object of the present invention to provide a multi-stage wire drawing device which is simple in design and requires little maintenance.
It is a further object of the present invention to provide a wire drawing device utilizing a drum having multiple sheaves in which slip and loss of power is substantially reduced compared with the devices heretofore known.
It is a particular object of the present invention to provide a drum for a multi-stage wire drawing machine comprising a plurality of sheaves over which the wire sequentially passes which sheaves may be rotated in a predefined ratio with respect to the extension of the wire.
These objects, other objects, together with numerous advantages of the present invention will be apparent from the following disclosure.